MOS solid-state imaging devices are commonly used in digital still cameras and digital video cameras. A semiconductor substrate of a MOS solid-state imaging device has a pixel area and a peripheral circuit area. The pixel area includes a plurality of pixels arranged in a matrix. The peripheral circuit area includes a peripheral circuit for reading signals from the pixels in the pixel area. In the MOS solid-state imaging device, a plurality of transistors are provided respectively for the pixels in the pixel area. The following describes the structure of the imaging device in detail, focusing only on one of the transistors in the pixel area. The pixel area of the semiconductor substrate is provided with source regions and drain regions. A wiring layer is formed over the semiconductor substrate so as to sandwich an insulating film therebetween. Also, a plurality of contact plugs penetrating the insulating film are formed. The contact plugs connect the wiring layer with each of the source and drain regions of the transistor in the pixel area.
Next, procedures for forming the contact plugs are described. First, after the source and drain regions of the transistor are formed in the pixel area of the semiconductor substrate, a metal film is formed over the semiconductor substrate. After that, the semiconductor substrate is subjected to heat treatment, so that the surfaces of the source and drain regions of the transistor is silicided (Hereinafter, the silicided area is called “silicide film”). After the heat treatment, the residue of the metal film, which is left unsilicided, is removed, and then the insulating film is formed over the semiconductor substrate. Afterwards, contact holes are formed by removing the part of the insulating film that covers the source and drain regions of the transistor, specifically by an etching method. Finally, a conductive material is implanted in each contact hole, whereby the contact plugs are formed on the silicide film.
As described above, in the procedures for forming the contract plugs, the source and drain regions of the transistor, which are to be in contact with one ends of the contact plugs, are silicide so that the contact resistance is reduced. This allows the MOS solid-state imaging device to operate at a high speed. As conventional technology relating to procedures for forming contract plugs, Patent Literature 1 discloses one technique.